This application is a U.S. National Phase under 35 U.S.C. § 371 of International Application No. PCT/US16/35016, filed May 31, 2016, which claims the benefit of U.S. Provisional Application No. 62/185,168, filed Jun. 26, 2015, and U.S. Provisional Application No. 62/168,731, filed May 30, 2015.
This invention relates in general to methods and fatty acid compositions for preparing triglycerides, and in particular for preparing triglycerides containing fatty acid diester functionality.
A number of different products are prepared from oils, including lubricants and other industrial fluids. Many of these products have traditionally been prepared from mineral based oils derived from petroleum. However, in recent years, there has been great interest in using oils derived from renewable feedstocks, including vegetable oils, algal oils and animal oils. The use of oils from renewable feedstocks is desirable to help reduce the world dependence on petroleum and other fossil-derived hydrocarbons. Moreover, these oils are typically biodegradable, which helps reduce the introduction of waste into the environment. Products produced from these oils may also have improved properties.
Triglycerides, also known as triacylglycerols or triacylglycerides, are the major component of oils derived from plants, algae and animals. A triglyceride is a compound consisting of three fatty acids esterified to a glycerol. The fatty acids may differ in length and may be saturated (no carbon-carbon double bonds), mono-unsaturated (one carbon-carbon double bond), di-unsaturated (two carbon-carbon double bonds) or tri-unsaturated (three carbon-carbon double bonds). Individual oils contain characteristic quantities of individual fatty acids that are randomly distributed among the triglyceride structures. For example, a typical soybean oil contains about 11% palmitic acid, 4% stearic acid (both saturated), 54% linoleic acid (di-unsaturated), 23% oleic acid (mono-unsaturated) and 8% linolenic acid (tri-unsaturated).
Whereas oils from renewable resources often have properties making them useful for preparing a variety of products, they also are very susceptible to air oxidation due to the oxidation of methylene groups adjacent to double bonds in their unsaturated fatty acids. These “allylic” methylene groups that are flanked by two double bonds (termed doubly allylic methylene groups) as found in linoleic and linolenic acids are especially prone to oxidation. Previous work (U.S. Pat. No. 8,357,643 and US patent application 2012/0129746) demonstrated that attachment of two ester groups to the original doubly bonded carbon atom in these fatty acid esters significantly reduces the oxidative susceptibility of their allylic methylene groups. This functionality in modified fatty acids is referred to as vicinal diester functionality or simply vicinal diesters.
An efficient method to prepare vicinal diesters in fatty acid esters is to first epoxidize all fatty acid double bonds and then react these epoxide groups with carboxylic acid anhydrides under basic conditions. However, the cost of carboxylic acid anhydrides can significantly contribute to the cost of products. The typical method to generate vicinal diesters from epoxides using less expensive carboxylic acids involves acidic catalysis. However, the reaction of carboxylic acids with linoleic and linolenic acid epoxides under acidic conditions gives rise to the production of non-desired tetrahydrofuranic (THF) diesters. The acid-catalyzed reaction of linoleic acid ester diepoxides with carboxylic acids to produce THF diesters is shown below:

THF diesters are non-desired since they are prone to oxidation at both methine sites adjacent to the THF ring oxygen atom.
It would be desirable to provide improved methods and improved fatty acid compositions for preparing triglycerides containing fatty acid vicinal diester functionality. It would further be desirable to provide triglycerides that are useful for preparing a variety of products, such as lubricants and other industrial oils, and that are resistant to air oxidation.